1. Field of the Invention
The invention pertains to a method for operating an adjustable stabilizer arrangement in a motor vehicle having a body and wheels, wherein the arrangement includes a pair of stabilizer sections connected to respective wheels on an axle of a vehicle, and an actuator having an electric motor for applying torque to the stabilizer sections.
2. Description of the Related Art
A stabilizer arrangement with an electric actuator is known from US 2007/0114733, where a rolling motion of the motor vehicle body is to be counteracted by means of automatic control of the actuator. A motor vehicle body, however, rolls not only when traveling around a curve but also while traveling straight ahead, i.e., when a wheel on one side is elastically deflected. It must be kept in mind here that the motor vehicle body moves at a frequency on the order of up to 1 Hz, whereas the frequency of the elastic deflection of a wheel can be as high as approximately 10 Hz.
According to the mathematical rules of oscillation theory, a stabilizer arrangement with an actuator represents a single-mass oscillation system with a pronounced resonance frequency in cases where the torque-transmission chain between the actuator and the stabilizer is highly efficient. The stabilizer forms the spring, and a rotor of the actuator is to be considered the mass, which has a certain mass inertia. The influence of the rotor mass becomes even greater when high-efficiency gearing is used between the actuator and the stabilizer. It is the square of the speed-reduction ratio of the gearing which enters into the calculation of the mass moment of inertia of the rotor. The resonance frequency in known systems is in the approximate range of 5-7 Hz, which is thus in the range of the oscillation frequency of the wheels. When the actuator is under open-loop or closed-loop control without consideration of these facts, the actuator executes very large control movements or exerts very large control forces, which are transmitted to the motor vehicle body and are perceived as uncomfortable by the passengers.
One solution to this problem could be to use low-efficiency gearing. By the use of low-efficiency gearing, there will be no resonance frequency as long as there is sufficient power loss (i.e., enough damping) in the gearing. One disadvantage of this solution is that, in an active sense, a large amount of engine power, corresponding to the power loss due to the gearing, is required to move the actuator. A second disadvantage is that the active stabilizer acts for the most part as a passive stabilizer when excited by the road. It can therefore be expected that much of the wheel excitation occurring on one side will be transmitted to the other side.
Another solution to the problem could be to increase the spring rate of the stabilizer. Because the modulus of elasticity of steel cannot be increased significantly, the spring rate must be increased by changing the cross section of the stabilizer. Increasing the cross section, however, is frequently associated with a disadvantageous increase in weight or in the amount of space occupied.
Another possibility would be to omit the actuator gearing and to use a very high-powered actuator instead. A high-powered actuator is either very expensive or very bulky.
It is proposed in DE 103 16 114 A1 that the signal components generated by the road simply be removed by sending them through a high-pass filter. This, however, leads to a loss of important data describing the rolling behavior of the motor vehicle body, and these data are therefore unavailable to the stabilizer control system.